Conventionally, each of an alumina sintered body, a zirconia sintered body, a silicon nitride sintered body and a silicon carbide sintered body, each of which is conventionally used as a structured article material, has been used in various technical fields, since it has both high strength and high hardness and is excellent in heat resistance and corrosion resistance. In the application where particularly high mechanical properties are required, the zirconia sintered body is used.
However, the zirconia sintered body is a material having high insulation properties. Thus, it is attempted to make the zirconia sintered body have a smaller volume resistivity by adding an electroconductive filler to the zirconia sintered body in order to apply the zirconia sintered body to a vacuum nozzle that is a member of an electronic parts mounting apparatus used for mounting electronic parts in chip form onto a circuit substrate or tweezers for handling magnetic heads, in which a treatment to remove static electricity is required.
The present applicant has already proposed a semi-conductive zirconia sintered body which comprises 60 to 90% by weight of ZrO2 containing a stabilizer and 10 to 40% by weight of at least one oxide of a metal selected from Fe, Co, Ni and Cr as an electroconductivity imparting agent, and which has a volume specific resistance in the range from 105 to 109 ohm-cm as shown in Patent Document 1. The semi-conductive zirconia sintered body can dissipate static electricity at a moderate rate without greatly reducing the mechanical properties of zirconia, so that it is not worn or damaged within a short time, and thus it can be suitably used over a long period of time.
Patent Document 2 proposes an ESD (electrostatic discharge) dissipative ceramic composition formed by sintering a mixture comprising a tetragonal zirconia polycrystal (TZP) and one or more resistivity modifiers for a sufficient time and at a sufficient temperature to achieve at least 99 percent of the theoretical density thereof, wherein the resistivity modifier comprises from about 5% by volume to 60% by volume of the mixture and is selected from the group consisting of the conductive materials, the semiconductive materials and the mixtures thereof; and wherein the ESD dissipative ceramic composition has a volume specific resistivity ranging from 103 to 1011 Ohm-cm, a flexural strength of at least 500 MPa, and a voltage decay time of less than 500 ms. Moreover, Patent Document 2 discloses ZnO, SnO2, ZrO2, Y2O3, Al2O3, ZrC, SiC, Fe2O3 and BaFe12O19, LaMnO3 and LaCrO3 as the resistivity modifier, and the ceramic composition has an L* color measurement of at least 50 using the CIE 1976 L*a*b* scale on an LKE colorimeter. According to the ESD dissipation ceramic of Patent Document 2, various demands for the resistivities relating to various applications are satisfied, and ESD dissipation ceramics having various colors can be provided.
Patent Document 3 proposes a zirconia sintered body comprising at least 80 to 95% by weight of ZrO2 containing an stabilizer and 5 to 20% by weight of TiO2 as a conductivity imparting agent and has a volume specific resistivity ranging from 106 to 1010 Ohm-cm. In addition, Patent Document 3 discloses, as its production method of a zirconia sintered body, a method comprising, performing sintering of the matrix under an oxidative atmosphere and performing a reduction sintering under an atmosphere containing Ar gas under a normal pressure or a high pressure, thereby adding a color similar to a black color to the zirconia sintered body. According to the zirconia sintered body, it is provided a zirconia sintered body, which is capable to dissipate static electricity at moderate rate without greatly reducing the mechanical properties of zirconia sintered body by using TiO2 which is a light metal oxide.
In addition, Patent Document 4 proposes a zirconia sintered body based on ZrO2/Y2O3, in which ZrO2 mainly comprises a crystal phase of a tetragonal phase zirconia, which provides an electroconductive zirconia sintered body having a high strength, Y2O3/ZrO2 molar ratio in the range from 1.5/98.5 to 4/96, Ti/Zr atom ratio in the range from 0.3/99.7 to 16/84, an average crystal grain diameter of zirconia not more than 2 μm (micrometers) and a porosity of the sintered body not more than 2%. Moreover, Patent Document 4 discloses, as its production method of the electroconductive and high strength zirconia sintered body, a method comprising sintering a raw matrix at a temperature in the range from 1250° C. to 1700° C. under an atmosphere comprising any of selected from the group consisting of an inert gas atmosphere, vacuum atmosphere, N2 atmosphere, hydrogen containing atmosphere and a hydrous atmosphere, thereafter subjecting the matrix to a HIP treatment below 1600° C. under an inert gas atmosphere. According to the electroconductive and high strength zirconia sintered body, it is capable to develop the electroconductivity by adding very slight amount of electroconductive substance to the zirconia sintered body, and to provide the electroconductive and high strength zirconia sintered body having improved properties without sacrificing the corrosion-resistant characteristic and the mechanical properties which are inherent to the matrix.    Patent Document 1: Japanese Patent Unexamined Publication No. 10-297968,    Patent Document 2: Japanese Patent Unexamined Publication No. 2006-199586,    Patent Document 3: Japanese Patent Unexamined Publication No. 2003-261376,    Patent Document 4: Japanese Patent Unexamined Publication No. 2005-206421.